In certain criminal proceedings it will be essential to establish that a person acted without lawful authority, lawful excuse or reasonable excuse. If the defendant, however, can show that they had authority or a lawful excuse to do the act in question then it will be a defence to a charge. The defendant must provide evidence, bearing the onus of proof and in the absence of such evidence then it will be presumed that no such authority or excuse exists.
The excuse turns on whether the purpose of the defendant was not forbidden by law and not that it was positively authorised by law. The case of Samuels v Nicholson helped establish a test for this defence. The test asks the question; did the defendant go beyond a mere matter of civil compensation and should be treated as a crime deserving punishment?
If a defendant honestly and reasonably believed in a state of affairs providing for a lawful excuse then this will be enough to constitute a defence.
The excuse used by a defendant will be judge objectively and general community standards will by applied to assess the strength of the excuse.